Recently the Chargers signed WR James Jones to replace, at least temporarily, Stevie Johnson as the team's 3rd WR. Jones has occupied virtually every slot on the depth chart since being drafted in the 3rd round in 2007, by Green Bay. Because of this, and the fact that he will likely be at most "target 4" (behind Allen, Benjamin, & Gates - not even counting Woodhead), I think examining efficiency/rate metrics would best allow us to project what kind of production Jones will bring to the team.
First off, what do we get out of Jones as an athlete - or rather, what did he bring when he entered the league? Honestly, nothing special. His 40 yard dash was pedestrian outside of a great 1.49s 10-yard-split at his pro-day, his jumps were good but not great, and his cone-drills were sub-standard. We can see the lack of shiftiness (represented by the cone drills) played a part in his career, where (from 2008-20102) he ran routes out of the slot only 8.4% of the time.
One thing Jones definitely brings to the field is, the fact that he brings himself to the field! He's averaged 15.1 games a season over his 9 season career, and played a full 16 games in 7 of those 9 seasons (77.8%). Since he has started 10 or more games a season, he has only missed 2 out of a possible 64 games.
Additionally, Jones has had only 1 negative-DVOA season since 2011 (his 1 year in Oakland, 2014). His career drop-% (drops/drops+catches) is 6.9% (very good), with nothing worse than 6.4% the past 4 seasons. He has been pretty good at gaining yards after the catch throughout his career, with an average YAC of 5.1 yards. (Granted, YAC is heavily influenced by the type of routes run, but with Whisenhunt's offense I think he will be set up to gain that YAC). The average point at which Jones caught his passes (aka: yards minus YAC) was 8.5 yards past the line - sometimes higher, sometimes lower, but generally in the mid-range. In 2015, 69.6% of his receptions were caught between the line and 20 yards downfield (& split evenly within that range). Jones is a chain mover - 63.5% of his receptions are for a 1st down, as well as a decent big-play threat - 19.6% of his receptions going for 20 or more yards.
There has been talk about Jones providing a valuable red-zone target, and the numbers add credence to that label. Over the course of his Packer career, Jones accumulated either the most or the 2nd most targets, receptions, yards & TDs in the red zone - all in spite of not being a primary receiver (51.7% start rate), playing with some very talented teammates (including Jordy Nelson, Randall Cobb, Greg Jennings & Donald Driver), and even not being a Packer one of the years of the sample. His TD% and AY/A (yards + 20*TD / targets) in the red zone were better than that of the remaining Packer players combined. Jones rates equally as positive when looking at passes within 10 yards of the end zone (ie: an actual 20 yards of field in which to catch a pass).
I know what you're thinking by now - he's had a pretty good career for a depth-receiver, but can we really expect any of that from a 32 year old player? Well, believe it or not, 2015 was one of his more efficient years. In his 8 years with a qualifying number of targets or receptions, Jones' 2015 ranked (among his career years):
3rd in DVOA
4th in drop%
5th in YAC**
1st in 1st-Down%
1st in 20yd+ % (setting a career high in total 20+ (18), despite only having his 4th highest total of receptions)
** But still 5.3 - he's been that good with YAC. He was also catching his passes (on average) further down field than ever before - 12.5 yards, for a career high in YPC (17.8).
If James Jones has a year similar to any he's had in the past 4 years with the Packers (Aaron Rodgers is a better comparison to Rivers than a rookie Derek Carr), I think this will have been a very solid signing.